Rotary hedge trimmer



Sept. 9, 1947. H. c. DRElscHERF 2,427,255 A ROTARY HEDGE vTRIMMER AFiled Dec, s. 194s y l. l/v l I rf, I I l r@ @il 23 22 ,f 24 /7 PatentedSept. 9, 1947 UNITED STATES .A OFFICE v 2,427,265 f ROTARY HEDGETRIMNIER Henry C. Dreischerf, Chicago, Ill.k Application December 3,1943, Serial No. 512,815

This invention relates to rotary hedgetrimmers, and is particularlyconcerned with improvements in the cutting blade and cutting guide usedin such trimmers.

Among the specific objects the following: (1) the provision of a newlightweight cutting blade carrying enlargements at either end whichconstitute relatively large cutting Vmasses capable of developing amaximum momentum, thereby producing more efficient operation;r (2) theprovision of cutting edges which render greater possibilities forsharpening, thereby contributing to better utilization of the bladeV andto increased life thereof; and (3) the provision of a guide carryingperipherally disposed projections disposed at an improved angle withrespect to the angle of the cutting edges of the blade, wherebyshrubbbery to be trimmed, that is, its twigs, leaves, etc., are gatheredand positioned radially inwardly under the impact of the blade'at kamore favorable angle of approach, thereby rendering more efficient workand resulting in neater trimming than is possible with prior apparatusof this type.

These and other objects of the invention will be brought out in detailin the description which is rendered below with reference to thedrawings. lIn these drawings,

Fig. 1 shows an embodiment of a hedge trimmer of the kind in which theinvention may be used;

Fig. 2 is a View of the trimmer along lines 2-2 in Fig. 1, showing anembodiment of the new cutting blade and the guide coacting therewith;and

Figs. 3 and 4 are enlarged views of cutting blade.

The trimmer shown in Fig. 1 is of the small type having a guide diameterof less than twelve inches, and a blade which is operated by a motorhaving a fraction of a horsepower, e. g., @le horsepower. Prior trimmersof such general structure frequently stop in operation, apparentlybecause the motor cannot overcome the brake forces presented by thecutting load. They have to be retracted from position in the shrubberyafter each stop-page so as to permit the motor to rotate the bladeagain. Such stop-start operation wastes time, is irritating to theoperator, damaging to the mechanism, and results in uneven cutting andgenerally wasteful and ineflicient operation. The invention avoids theseand other drawbacks in a manner pointed out below, first with referenceto Fig. l. 1 y'Iflumeral Il indicates a small electric motor the new ofthe invention are 7 Claims. (Cl. 30-206) y mounted on the tubular neckI2 which carries a generally circular guide plate I3 and a radiallyrearwardly projecting arm I4. The later is provided with an angularextension I5 to which is attached the bottom guard plate I6 by means ofan arm .I1 secured by a bolt I8 on the extension I5. Another arm I9projects from the plate I6 at the forward end thereof and carries alaterally disposed blade guard 20.which is usually referred to as lingerguard. This latter guard prevents edgewise contact of the rotating bladewith objects adjacent the hedge'to be trimmed, e. g., walls and fences.The vbottom guard plate I6 keeps the cutting blade a desired distanceabove the base of the cutting plane, e. g., the ground, and protectsitagainst damage from and interference with vobjects at the bottom. Themotor shaft projects through the guide plate I3 and carries the cuttingblade 2|. Numeral 30 indicates a shell attached to the structure by asuitable clamp and holding a rearwardly projecting handle 3 I. Numeral32 indicates the cord for the electric motor. j

"The cutting blade rof prior trimmers of this type is usually made ofsuitable at sheet material and shaped with the longitudinal edges nearlyinf parallel. One side at each end of the blade is usually cut or groundat an angle to the plane of the blade body to form a cutting edge. Thereare thus only two cutting edges, one at either endV of the blade, andthe blade is therefore always used so Vas to'rotate in the samedirection. Dulling ofthe cutting edges requires stopping of theoperationA andsharpening of the blade before the operation can beresumed. The life of such orthodox cutting blade is short because therelatively narrow masses at its ends are quickly ground'off by thesharpening that is from time to time required. The structure of such acutting blade as made heretofore presents a relatively heavy mass in andtoward the center, requiring operating torque ofthe small motor which isunder certain'conditions too great for its rating. Hence the frequentstopping of operation, as previously mentioned. i

Theguide plate usually found in prior structures 'is' provided' withperipheral circumferentially .spaced cutouts forming peripherallydisposed teeth "or projections which extend either in parallel with oneanother, in the form of a grid, or at an angle which' intersects theaxis of the apparatus.'l The angle of the guideV plate projectionsis notvdisposed'mold devices with a View p toward facilitating' the cuttingoperation in coaction with the rotating cutting blade, 1j

'The new blade structure and the structure of the new guide plate, aswell as coaction of these elements, are best described by referring toFigs. 2-4, inclusive.

The new blade is made of flat steel sheet of suitable thickness andquality, cut, machined or stamped therefrom (cast blades may beemployed), and comprises a central mounting section 22, outwardlyslightly tapering relatively light arms 23-24 extending radiallyoutwardly from the central mounting section, and enlargements 25-26, oneat each end of the arms 23- 24, which constitute the cutting masses ofthe structure. The result is a relatively lightweight blade requiringsmall torque for operation and disposing large masses at opposite endswhich develop relatively great momentum exactly where the force of suchmomentum is needed and Where it can enhance the operation, namely, atthe points where the actual cutting takes place and where brake forcesare applied by contact with the shrubbery, grass or the like, which isto be trimmed.

Each enlargement is shaped in the form of a segment. The sides ofV eachseg-ment are cut radially inwardly with the lines thereof, when radiallyinwardly projected, intersecting about midway of the corresponding arms23-'24 thus forming a mass at each end of the blade which is shaped likethe frustum of a cone, with the base projecting outwardly and the smallend merging with the inwardly extending arm. The edges of theseenlargements are cut or ground at an angle to the general plane of theblade body forming at each end of the blade a pair of oppositelydisposed inwardly tapering cutting edges, one on each side of thecorresponding enlargement.

The top guide plate I3 is made Vof suitable sheet material, -generallycircular in shape, and provided with a number of peripherally disposedteeth or projections 35. Each projection or tooth is provided with astraight edge disposed so as to form, in coaction with the cutting edgeof the blade incident to the rotation thereof, an acute radiallyinwardly widening angle. The far side of each projection, viewed in thedirection of rotation of the cutting blade, forms a curved edge adaptedt-o guide shrubbery and the like into the circumferential spaces betweenadjacent projections.

In operation, the objects to be trimmed, e. g., leaves and twigs, enterthe circumferential spaces between the teeth or projections 35. Theblade rotates, driven by the motor Il, and as the angularly disposedinwardly tapering cutting edges sweep across the spaces between theprojections they cut the leaves and the like, trimming the hedge asdesired. The momentum developed by the blade due to the cutting massesat its opposite ends facilitates the operation by adding the force ofthese masses to the rotation imparted by the motor. The kpossibility forstopping is therefore greatly diminished and is in normal operationeliminated.

The manner in which the cutting edges are disposed on the blade providesa more favorable angle of approach for cutting, and the manner in whichthe straight edges of the teeth or projections on the guide plate aredisposed furnishes a more favorable angle `for holding and nestling theleaves and the `like for the cutting operation of the blade. Theresulting coaction between the inwardly tapering cuttingedges of theblade and the inwardly angularly extending straight edges of the guideprojections .tends to move the'leaves to Cil 4 be trimmed radiallyinwardly to position them for efficient cutting. The cutting approach ofthe cutting edges is not perpendicular to the objects to be cut, buttangential thereto, reducing impact forces and increasing true cuttingand slicing forces which are more efficient for the intended purpose.

The provision of two cutting edges at each end of the blade furnishesgreater operating and sharpeningpossibilities. In case of dulling of thetwo cutting edges which are initially active (assuming that a newlysharpened blade is being used), all that is necessary is to turn theblade around so as to utilize the two remaining sharp cutting edges.Trimming can then proceed. The effective operation time, as comparedwith old blades provided with only two cutting edges, one at each endthereof, is thus doubled.

The relatively large masses at the outer ends of the new blade increasethe life thereof because they furnish more material for sharpening.

Changes may be made within the scope and spirit of the following claimsin which I have dened what I consider new and desire to have pro tectedby Letters Patent of the United States.

I claim:

l. A blade made of generally at material for use in a rotary hedgetrimmer of the class described, which includes a motor and a shaftrotated thereby, said blade comprising a central mounting section forsuitable attachment to the shaft of said motor, radially outwardlyproject- .ing farms each of outwardly `diminishing width extending fromsaid mounting section, an enlargement carried by each of said arms atthe cuter end thereof and 'forming a mass thereat of radially outwardlyincreasing width, the sides of each of said Venlargements being beveledat an angie to the plane of the body of said blade to form a reversibleblade with a pair of oppositely dispcsed inwardly converging cuttingedges, said :enlargements forming masses at the outer ends of said armswhich increase the momentum of the blade responsive to rotation thereoffor the purpose of increasing the cutting force thereof.

A relatively lightweight cutting blade made lof generally fiat materialfor use in a rotary hed-ge trimmer of the class described, whichincludes a motor driven shaft, the masses of said blade bein-gdistributed in such a manner as to combi-ne great strength-and cuttingforce with small total weight, the blade comprising a central mountingsection for suitable attachment to said motor driven shaft, radiallyoutwardly projecting arms lextending from said mounting section, thewidth of said arms diminishing radially symmetrically voutwardly for thepurpose of diminishing the total weight of the blade and thetorque'required for the rotation thereof, and an enlargement at theouter end of each of said arms forming a mass thereat of radiallyoutwardly increasing width and carrying the cutting edges of the blade,the masses of said enlargements providing for greater momentum of theblade and for increased cutting force thereof when said blade is rotatedby said motor driven shaft.

3. The structure defined in `claim 2, wherein the enlargement at the endof each of said arms is provided with inwardly converging edges forminga body similar to the frustum of a cone the small end of which mergeswith the Icorresponding arm of the blade.

4. The structure defined Vin claim 2, wherein the enlargement at the endof each of said arms is formed by a body which is appreciably wider thanthe corresponding arm from which it extends and forms thereat theoutline of a body with outwardly flaring edges, each of said edges beingbeveled at an angle to the general plane of the body of the blade toform the cutting edges thereof.

5. In a rotary hedge trimmer of the class described, which includes amotor and a shaft driven thereby, a blade comprising a central mountingsection for suitable attachment to said shaft and arms radiallyoutwardly extending therefrom and carrying cutting edges at the outerends thereof, a guide plate of generally circular outline carryingperipherally disposed projections extending therefrom atcircumferentially spaced intervals, each of said projections having aninwardly directed substantially straight edge forming an acute anglewith the center line through the axis of the guide plate, the straightedge of each of the projections of the guide plate coacting with thecutting edges of the blade attached to said motor driven shaft for thepurpose of forming an acute angle therewith.

6. In a rotary hedge trimmer of the class described, which includes amotor and a shaft driven thereby, a blade comprising a central mountingsection for suitable attachment to said shaft and arms radiallyoutwardly extending therefrom and carrying cutting edges at the outerends thereof, a guide plate of generally circular outline carryingperipherally disposed projections extending therefrom atcircumferentially spaced intervals, each of said projections having aninwardly directed substantially straight edge forming an acute anglewith the center line through the axis of the guide plate, the straightedge of each of the projections of the guide plate coacting with thecutting edges of the blade attached to said motor driven shaft for thepurpose of form-ing an acute angle therewith, whereby objects to betrimmed including leaves, twigs, shrubbery and the like are drawninwardly and nestle within the circumferential spaces between saidprojections incident to approach of the cutting edges of the bladeresponsive to rotation thereof.

'7. The structure defined in claim 5, wherein the blade is provided withan enlargement at the outer end of each of the radially projecting armsthereof, said enlargements carrying the cutting edges, the masses ofsuch enlargements imparting to the blade a greater momentum to increasethe cutting force of said cutting edges responsive to the rotation ofsaid blade.

HENRY C. DREISCHERF.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS

